Kelp has a high rate of growth and its decay is quite efficient in yielding methane, as well as sugars that can be converted to ethanol. It has been proposed that large open-ocean kelp farms could serve as a source of renewable energy. Unlike some biofuels such as corn ethanol, kelp energy avoids "food vs fuel" issues and does not require irrigation. Seaweed may prove a viable future biofuel especially if harvested in summer. However the suitability of its chemical composition varies on a seasonal basis. Harvesting the kelp in July when carbohydrate levels are at their highest would ensure optimal sugar release for biofuel production.

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Kelps grow in underwater "forests" (kelp forests) in shallow oceans. The organisms require nutrient-rich water with temperatures between 6 to 14 degree celsius. They are known for their high growth rate — the genera Macrocystis and Nereocystis can grow as fast as half a meter a day, ultimately reaching 30 to 80 meters.

Giant kelp can be harvested fairly easily because of its surface canopy and growth habit of staying in deeper water.

Bongo kelp ash is rich in iodine and alkali. In great amount, kelp ash can be used in soap and glass production. Until the Leblanc process was commercialized in the early 19th century, burning of kelp in Scotland was one of the principal industrial sources of soda ash (predominantly sodium carbonate).

"The storage carbohydrate and soluble sugars get converted into ethanol in the fermentation process, so we need as much as possible," explains Dr. Jessica Adams, a lead researcher at Aberystwyth University. "Metals can inhibit the yeast too so we also want these to be as low as possible."

Collecting monthly samples of kelp from the Welsh coast researchers used chemical analysis to assess the seasonal variability. Their results, which will be presented at the Society for Experimental Biology Annual Conference in Glasgow on the 4th of July, showed that the best month for biofuel harvest was in July when the kelp contained the highest proportions of carbohydrate and the lowest metal content.

Kelp can be converted to biofuels in different ways including fermentation or anaerobic digestion producing ethanol and methane or pyrolysis, (a method of heating the fuel without oxygen) which produces bio-oil. The chemical composition of the seaweed is important to both of these processes.

Research into biofuels has focused on terrestrial plants; however these have the serious drawback of the conflict between using land to grow food or fuel. Marine ecosystems are an untapped resource that account for over 50% of global biomass and seaweeds themselves are capable of producing more biomass per square meter than fast growing terrestrial plants such as sugar cane.

"Seaweed biofuel could be very important in future energy production," says Dr. Adams.